Gas dissolved water producing apparatus and method thereof and ultrasonic cleaning equipment and method thereof

ABSTRACT

The object of the present invention is to provide a gas dissolved water producing apparatus which can produce a gas dissolved water  31  having a concentration of a dissolved solution gas  3  not greater than a saturated concentration rapidly and efficiently.  
     The apparatus comprises a gas dissolving section, a gas channel for guiding a gas into the dissolving section, a first water channel for guiding a water into the dissolving section, a gas dissolved water discharge channel, and a second water channel for guiding the water without passing through the dissolving section. The second water channel joins the gas dissolved water discharge channel to control the solution gas dissolved in the gas dissolved water can be controlled to a prescribed level of concentration.

TECHNICAL FIELD

[0001] The present invention relates to an aqueous solution producingapparatus, which contains a gas dissolved therein, (hereafter referredto as gas dissolved water producing apparatus) and a method thereof, andin particular to a gas dissolved water producing apparatus and a methodthereof for producing a gas dissolved water used in precisionmachineries, electronic industries and medical and food industries.

[0002] BACKGROUND OF ARTAs shown in FIG. 10, in a prior art gasdissolved water producing apparatus 201, a gas to be dissolved(hereafter referred to as solution gas) 103 is typically introduced intoan outer side of a hollow fiber membrane 102 incorporated in aprocessing tank 111, which is then dissolved through the hollow fibermembrane 102 into a water to be treated 104 introduced into an innerside of the hollow fiber membrane 102, so as to produce a gas dissolvedwater 105.

[0003] The water to be treated 104 is fed by a pump 117 at a prescribedflow rate “q” to the inner side of the hollow fiber membrane 102 via afilter 118 and a flow meter 119. A flow rate signal 120 (illustrated bya broken line in the drawing) from the flow meter 119 is sent to acontroller 121, which in turn sends a flow rate control signal 122(illustrated by another broken line in the drawing) to a motor (notshown) for driving the pump 117, which is equipped with a revolutionspeed control unit (not shown), and thereby the revolution speed of themotor can be controlled such that the pump 117 provides a prescribedflow rate “q”.

[0004] The solution gas 103 passes through the flow meter 116, where aflow rate is controlled to a prescribed level, and is sent to an outerside of the hollow fiber membrane 102 approximately under an ambientpressure, and dissolved in water to be treated 104 through the hollowfiber membrane 102, while a residual gas is decomposed in an exhaust gasdecomposing tower 130 with an aid of a catalyst (not shown) and emittedas an exhaust gas 106.

[0005] In the conventional gas dissolved water producing apparatusdiscussed above, a concentration of a solution gas dissolved in aproduced aqueous solution (gas dissolved water) is a saturatedconcentration of a solution gas under a pressure for supplying thesolution gas (typically an ambient pressure, that is a cleaning pressureunder which cleaning is performed by using the gas dissolved water).However, in precision machineries, electronic industries, and medicaland food industries, gentle cleaning of workpieces may be required so asto avoid any damage. To Thus, it is desired to produce a gas dissolvedwater having a concentration of solution gas in a gas dissolved waternot greater than a saturated concentration at a cleaning pressure. Theneed for such a cleaning process is especially necessary for devicewafers such as semiconductor wafers, which have micro-fabricated wiring;and there is therefore an increasing demand for cleaning by use offunctional water, such as water containing nitrogen, water containingozone, or water containing oxygen, with the concentration controlled toa desired level below a saturated concentration.

[0006] Such a gas dissolved water can be produced by, for example, thefollowing procedures. That is, after the solution gas has been suppliedto the outer side of the hollow fiber membrane, supply of the solutiongas is suspended, with only the water to be treated being continuouslysupplied to dissolve the solution gas into the water to be treated.Consequently, pressure in the outer side of the hollow fiber membranedecreases, and the solution gas dissolves into the water to be treatedand reaches a saturated concentration under the decreased pressurelevel. Once the concentration has reached a desired value, the solutiongas is again supplied into the outer side of the hollow fiber membrane,such that the pressure level can be maintained. As a result, theconcentration of the solution gas dissolved in the gas dissolved wateris made lower than a saturated concentration in the case of supplyingthe solution gas under ambient pressure. However, disadvantageously, ittakes a long time for a pressure in the outer side of the hollow fibermembrane to reach the above-described pressure which is lower thanambient pressure. Besides, there is also a fear that a gas other thanthe targeted solution gas may become mixed with the solution gas under apressure lower than ambient pressure.

[0007] The present invention has been made in light of the situationdescribed above, and has as its object the provision of a gas dissolvedwater producing apparatus and a method therefor which is capable ofproducing a gas dissolved water having a concentration of a dissolvedsolution gas not greater than a saturated concentration under ambientpressure, both rapidly and efficiently.

DISCLOSURE OF INVENTION

[0008] To accomplish the object described above, according to thepresent invention as defined in claim 1, there is provided a gasdissolved water producing apparatus 1, in which a solution gas 3 isdissolved in a water to be treated 4 so as to produce a gas dissolvedwater 5, the apparatus comprising, as shown in FIG. 1: a dissolvingsection 11 for dissolving the solution gas 3 into the water to betreated 4; a solution gas supply channel 12 for guiding the solution gas3 into the dissolving section 11; a first supply channel for the waterto be treated 13 for guiding the water to be treated 4 into thedissolving section 11; a gas dissolved water discharge channel 14 forguiding the gas dissolved water 5 from the dissolving section 11; and asecond supply channel for the water to be treated 15 for guiding thewater to be treated 4 without passing through the dissolving section 11,wherein the second supply channel for the water to be treated 15 joinsthe gas dissolved water discharge channel 14, and the water to betreated 4 which has been guided through the second supply channel forthe water to be treated 15 dilutes the gas dissolved water 5 so that thesolution gas dissolved in the gas dissolved water 5 can be controlled toa prescribed level of concentration.

[0009] In the configuration described above, the apparatus includes thesolution gas supply channel 12, the first supply channel for the waterto be treated 13, the second supply channel for the water to be treated15 and the gas dissolved water discharge channel 14, in which the secondsupply channel for the water to be treated 15 joins the gas dissolvedwater discharge channel 14, and thus the solution gas dissolved in thegas dissolved water 5 can be diluted to a prescribed level ofconcentration with the water to be treated 4 which has been guidedthrough the second supply channel for the water to be treated 15. As aresult, the apparatus is able to produce a gas dissolved water 31 havinga concentration of dissolved solution gas not greater than a saturatedconcentration, both rapidly and efficiently.

[0010] According to the present invention as defined in claim 2, thereis provided a gas dissolved water producing apparatus 1 in accordancewith claim 1, in which, as shown in FIG. 1, the second supply channelfor the water to be treated 15 is branched-off from the first supplychannel for the water to be treated 13 so as to form a bypass channel 15for bypassing the dissolving section 11.

[0011] With this configuration, since the second supply channel for thewater to be treated 15 branches-off from the first supply channel forthe water to be treated 13 to form the bypass channel 15 for bypassingthe dissolving section 11, it is possible to simplify the channelconfiguration.

[0012] According to the present invention as defined in claim 3, thereis provided a gas dissolved water producing apparatus in accordance withclaim 1 or 2, in which, as shown in FIG. 1 and FIG. 2, the dissolvingsection 11 comprises a hollow fiber membrane 2 wherein the solution gas3 is introduced into one side of the hollow fiber membrane 2, and thewater to be treated 4 is introduced into the other side of the hollowfiber membrane 2 so as to generate the gas dissolved water 5.

[0013] The dissolving section 11 comprises the hollow fiber membrane 2,and the solution gas 3 is introduced into one side of the hollow fibermembrane 2 and the water to be treated 4 is introduced into the otherside of the hollow fiber membrane 2, thereby generating the gasdissolved water 5. As a result, the apparatus is able to generate a gasdissolved water rapidly and efficiently that includes no residual minuteair bubbles or impurities. It is to be noted that one side of the hollowfiber membrane designates either the inner or the outer side thereof andthe other side of the hollow fiber membrane designates a side oppositeto said one side, either the outer or the inner side thereof.

[0014] According to the present invention as defined in claim 4, thereis provided a gas dissolved water producing apparatus 1 in accordancewith either one of claim 1 to 3, the apparatus further comprising, asshown in FIG. 1: either a first flow rate regulating means 23 or asecond flow rate regulating means 24, the first flow rate regulatingmeans 23 being disposed in the first supply channel for the water to betreated 13 at a downstream side of a branch section 13A or in the gasdissolved water discharge channel 14 at an upstream side of a joiningsection 14A where the second supply channel for the water to be treated15 joins the gas dissolved water discharge channel 14, and functioningto regulate a flow rate Q1 of the water to be treated 4 flowing throughthe dissolving section 11, and the second flow rate regulating means 24being disposed in the bypass channel 15 and functioning to regulate aflow rate Q2 of the water to be treated 4 bypassing the dissolvingsection 11; a dissolved solution gas concentration measuring means 26disposed in the gas dissolved water discharge channel 14 at a downstreamside of the joining section 14A for measuring the dissolved solution gasconcentration in the gas dissolved water 31; and a second control means28 for controlling either the first flow rate regulating means 23 or thesecond flow rate regulating means 24, whichever has been disposed, basedon the dissolved solution gas concentration measured by the dissolvedsolution gas concentration measuring means 26, so that the dissolvedsolution gas concentration can be controlled to the prescribed level.

[0015] By the configuration described above, since the apparatuscomprises either the first flow rate regulating means 23 or the secondflow rate regulating means 24, the dissolved solution gas concentrationmeasuring means 26, and the second control means 28, the second controlmeans 28 controls either the first flow rate regulating means 23 or thesecond flow rate regulating means 24 based on a dissolved solution gasconcentration measured by the dissolved solution gas concentrationmeasuring means 26 so that a dissolved solution gas concentration can becontrolled to a prescribed level, to thereby enable the apparatus toproduce the gas dissolved water 31 having a dissolved solution gasconcentration not greater than a saturated concentration both rapidlyand efficiently. It is to be understood that the gas dissolved waterproducing apparatus 1 may comprise both of the means 23, 24, the firstflow rate regulating means 23 and the second flow rate regulating means24, and in such a case both of means 23 and 24 can be controlled in sucha way that the dissolved solution gas concentration, as measured, can becontrolled to a prescribed level.

[0016] To accomplish the object described above, according to thepresent invention as defined in claim 5, there is provided a gasdissolved water producing method comprising, as illustrated in FIG. 1: afirst process for introducing the solution gas 3 into the dissolvingsection 11 where the solution gas 3 is to be dissolved into the water tobe treated 4; a second process for introducing the water to be treated 4into the dissolving section 11; a third process for dissolving thesolution gas 3 into the water to be treated 4 in the dissolving section11 to produce the gas dissolved water 5; and a fourth process for mixingthe water to be treated 4 not passing through the dissolving section 11into the gas dissolved water 5 so that the solution gas 3 dissolved inthe gas dissolved water 31 after the mixing process can be controlled tothe prescribed level of concentration.

[0017] According to the present invention as defined in claim 6, thereis provided a gas dissolved water producing method in accordance withclaim 5, in which, as shown in FIG. 1, control in the fourth process isperformed by controlling a ratio of the flow rate Q1 of the water to betreated 4 passing through the dissolving section 11 to the flow rate Q2of the water to be treated 4 not passing through the dissolving section11.

[0018] To accomplish the object described above, according to thepresent invention as defined in claim 7, there is provided an ultrasoniccleaning equipment 101 comprising, as shown in FIG. 6 and FIG. 7: a gasdissolved water producing apparatus 1 as defined in any one of claims 1to 4; and an ultrasonic wave transmitting device 157 for impartingultrasonic energy to the gas dissolved water 31 when a workpiece to becleaned W1 is cleaned with the gas dissolved water 31 produced by thegas dissolved water producing apparatus 1.

[0019] With such a configuration, since the apparatus includes the gasdissolved water producing apparatus 1, as defined in any one of claims 1to 4, and the ultrasonic wave transmitting device 157, and ultrasonicenergy is imparted to the gas dissolved water 31, which has beenproduced by the gas dissolved water producing apparatus 1 in accordancewith either one of the claim 1 to 4, when the workpiece to be cleaned W1is to be cleaned with the gas dissolved water 31, the gas dissolvedwater 31 to which ultrasonic energy has been imparted can be used as acleaning liquid, and the gas dissolved water 31 having a concentrationcontrolled to the saturated concentration is suitable for use as acleaning liquid, whereby the workpiece to be cleaned W1 can be moreeffectively cleaned. To accomplish the object described above, accordingto the present invention as defined in claim 8, there is provided anultrasonic cleaning method comprising: a producing process for producingthe gas dissolved water according to the gas dissolved water producingmethod as defined in claim 5 or 6; an energy imparting process forimparting the ultrasonic energy to the gas dissolved water which hasbeen produced by the producing process; and a cleaning process forcleaning the workpiece to be cleaned, by using the gas dissolved waterto which the ultrasonic energy has been imparted in the energy impartingprocess, as the cleaning water.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a flow diagram illustrating a configuration of a gasdissolved water producing apparatus of an embodiment according to thepresent invention;

[0021]FIG. 2 is a schematic sectional view illustrating a configurationof a processing tank;

[0022]FIG. 3 is a diagram illustrating an experimental data of anitrogen gas concentration as a function of time, in the case wherenitrogen gas is used as a solution gas for producing a gas dissolvedwater with a nitrogen gas concentration of 6 ppm, in the gas dissolvedwater producing apparatus of the present invention;

[0023]FIG. 4 is a diagram illustrating other experimental data of anitrogen gas concentration as a function of time, in the case where thenitrogen gas is used as the solution gas for producing the gas dissolvedwater with the nitrogen gas concentration of 10 ppm, in the gasdissolved water producing apparatus of the present invention;

[0024]FIG. 5 is a diagram illustrating still another experimental dataof a nitrogen gas concentration as a function of time, in the case wherethe nitrogen gas is used as the solution gas for producing the gasdissolved water with the nitrogen gas concentration of 13 ppm, in thegas dissolved water producing apparatus of the present invention;

[0025]FIG. 6 is a perspective view of an ultrasonic cleaning equipmentfor wafer for cleaning the wafer by using a gas dissolved water producedby the gas dissolved water producing apparatus of FIG. 1;

[0026]FIG. 7 is a sectional view of a mega sonic cleaning nozzleemployed in the wafer cleaning equipment of FIG. 6;

[0027]FIG. 8 is a block diagram illustrating a configuration of anultrasonic cleaning equipment for wafer according to another embodimentof the present invention;

[0028]FIG. 9 is a perspective view of a cleaning liquid supply nozzleemployed in the ultrasonic cleaning equipment of FIG. 8; and

[0029]FIG. 10 is a flow diagram illustrating a configuration of a gasdissolved water producing apparatus according to a prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0030] Preferred embodiments of the present invention will now bedescribed below with reference to the attached drawings. It is to beappreciated that in respective drawings, those parts which are the sameor similar to one another are designated by the same or similarreference numerals, and any duplicated descriptions will be omitted.

[0031] A configuration of a gas dissolved water producing apparatus 1according to the present invention will be described with reference toFIG. 1. The gas dissolved water producing apparatus 1 comprises aprocessing tank 11 serving as a dissolving section with a hollow fibermembrane 2 (see FIG. 2) incorporated therein, a solution gas supplypiping 12 serving as a solution gas supply channel for delivering asolution gas 3 from a solution gas source 7, a supply piping for a waterto be treated 13 serving as a first supply channel for the water to betreated for delivering the water to be treated 4 from a source of thewater to be treated 8, a gas dissolved water discharge piping 14 servingas a gas dissolved water discharge channel for guiding a gas dissolvedwater 5, a bypass piping for the water to be treated 15 serving as abypass channel, which branches off from the supply piping for the waterto be treated 13 and bypasses the processing tank 11 or the hollow fibermembrane 2 to join the gas dissolved water discharge piping 14, and agas dissolved water drain piping 25 branched off from the gas dissolvedwater discharge piping 14.

[0032] As shown in FIG. 2, the processing tank 11 has a first inletnozzle 41 disposed in a lower side peripheral portion thereof, a firstoutlet nozzle 42 disposed in an upper side peripheral portion thereof, asecond inlet nozzle 43 disposed in a top portion thereof, and a secondoutlet nozzle 44 disposed in a bottom portion thereof, wherein aplurality of hollow fiber membranes 2 formed into hollow cylinder with athinner wall thickness are arranged in a vertical direction in theprocessing tank 11 so as to be incorporated therein.

[0033] The solution gas supply piping 12 is connected to the first inletnozzle 41 of the processing tank 11 to communicate with the outer sideof the hollow fiber membrane 2. The supply piping for the water to betreated 13 is connected to the second inlet nozzle 43 of the processingtank 11 to communicate with the inner side of the hollow fiber membrane2. The gas dissolved water discharge piping 14 is connected to thesecond outlet nozzle 44 of the processing tank 11 to communicate withthe outer side of the hollow fiber membrane 2. To the first outletnozzle 42 of the processing tank 11 is connected an exhaust gas piping45, which will be explained later.

[0034] Referring again to FIG. 1, explanation will be continued. Thebypass piping for the water to be treated 15 branches off at a branchsection 13A from the supply piping for the water to be treated 13 andjoins the gas dissolved water discharge piping 14 at a joining section14A. Accordingly, assuming that a flow rate of the water to be treated 4supplied to the supply piping for the water to be treated 13 isdesignated as “Q”, a flow rate of the water to be treated 4 suppliedfrom the supply piping for the water to be treated 13 to the inner sideof the hollow fiber membrane 2 is designated as “Q1”, and a flow rate ofthe water to be treated 4 branching off from the supply piping for thewater to be treated 13 and flowing through the bypass piping for thewater to be treated 15 is designated as “Q2”, then a relationshipQ=Q1+Q2 is established (including a case of Q1 or Q2 being equal to 0).In this embodiment, the flow rate of the gas dissolved water 5 flowingfrom the inner side of the hollow fiber membrane 2 into the gasdissolved water discharge piping 14 is Q1, and the flow rate of the gasdissolved water 31 which is discharged from the gas dissolved waterdischarge piping 14 after the water to be treated 4 having the flow rateQ2 joins and dilutes the gas dissolved water, is Q.

[0035] It is to be noted that the gas dissolved water exited from theprocessing tank 11 and flowing through the gas dissolved water dischargepiping 14 that has not yet reached the joining section 14A is indicatedby the reference numeral 5, while the gas dissolved water that hasjoined the water to be treated 4 which has not passed through theprocessing tank 11, at the joining section 14A and has been dilutedthereby is indicated by the reference numeral 31. It is to be alsounderstood that even if a flow rate of the water to be treated 4 notpassing through the processing tank 11 is zero and thus there is nodilution to be conducted, the gas dissolved water flowing through thegas dissolved water discharge piping 14 in the downstream side of thejoining section 14A is still represented by the reference numeral 31.

[0036] A solution gas flow regulator 16 is installed in the solution gassupply piping 12 so as to regulate the flow rate of the solution gas 3supplied to the outer side of the hollow fiber membrane 2, to theprescribed value. A pump 17 driven by a motor (not shown) is installedin the supply piping for the water to be treated 13 so as to pump thesupplied water to be treated 4 into the processing tank 11. A filter 18is installed in the supply piping for the water to be treated 13 at adownstream side of the pump 17 to eliminate foreign substances includedin the water to be treated 4. A flow meter 19 is installed in the supplypiping for the water to be treated 13 at a downstream side of the pump17 for functioning as a flow rate measuring means, and the flow meter 19sends a flow rate signal 20 (indicated by the broken line in thedrawing) to a first controller 21 functioning as the first controlmeans, which in turn sends a flow rate control signal 22 (indicated alsoby the broken line in the drawing) to the motor (not shown) equippedwith a revolution speed control unit (not shown)(the signal is shown tobe sent to the pump 17 in the drawing), thereby controlling therevolution speed of the motor so that the discharge flow rate of thepump 17, i.e., the supply flow rate Q of the water to be treated 4 tothe gas dissolved water producing apparatus 1, can be regulated to theprescribed flow rate. It is to be noted that the pump 17, the filter 18and the flow meter 19 are all located in the upstream side of the branchsection 13A.

[0037] A first flow regulator for the water to be treated 23 functioningas the first flow rate regulating means is installed in the supplypiping for the water to be treated 13 at a downstream side of the branchsection 13A, and the second flow regulator for the water to be treated24 functioning as the second flow rate regulating means is installed inthe bypass piping for the water to be treated 15. Although the firstflow regulator for the water to be treated 23 may be installed in thesupply piping for the water to be treated 13 either at an upstream or adownstream side of the hollow fiber membrane 2, the installation in thedownstream side of the hollow fiber membrane 2, as illustrated, ispreferable because a water pressure applied to the hollow fiber membrane2 can be increased, which means that the solution gas 3 can be suppliedat relatively higher pressure while maintaining the relationship: thewater pressure of the water to be treated 4>the gas pressure of thesolution gas 3.

[0038] The gas dissolved water discharge piping 14 is connected to a gasdissolved water concentration meter 26 serving as a dissolved solutiongas concentration measuring means for measuring the concentration of thesolution gas 3 dissolved in the gas dissolved water 31, and the gasdissolved water concentration meter 26 sends a concentration signal 27to a second controller 28 serving as a second control means. The gasdissolved water concentration meter 26 measures the concentration of thegas dissolved water 31 after having been diluted. The second controller28 sends a second flow rate control signal 29 to the first flowregulator for the water to be treated 23 and the second flow regulatorfor the water to be treated 24. Upon receiving the second flow ratesignal 29, the first and the second flow regulators of the water to betreated 23 and 24 regulate the ratio of the flow rate Q1 of the water tobe treated 4 flowing through the first flow regulator for the water tobe treated 23 to the flow rate Q2 of the water to be treated 4 flowingthrough the second flow regulator for the water to be treated 24, sothat the concentration detected by the gas dissolved water concentrationmeter 26 can be controlled to the prescribed concentration.

[0039] The exhaust gas 6 exiting from the outer side of the hollow fibermembrane 2 is exhausted via an exhaust gas piping 45, and in a case thatthe exhaust gas contains a noxious gas, such an exhaust gas should betreated in a gas decomposing tower 30 filled with catalyst or the like(not shown) to decompose the noxious gas before emitting to theatmosphere.

[0040] An operation of the gas dissolved water producing apparatus 1will now be described.

[0041] The solution gas 3 is supplied to the solution gas supply piping12, and the supplied solution gas 3 is, after the flow rate thereofhaving been regulated by the solution gas flow regulator 16, deliveredto the outer side of the hollow fiber membrane 2 incorporated in theprocessing tank 11, at a prescribed flow rate. The water to be treated 4is supplied to the supply piping for the water to be treated 13, and thesupplied water to be treated 4 is compressed by the pump 17 and ispassed through the filter, where the foreign substances, if any,included in the water to be treated 4 are eliminated, and furtherthrough the flow meter 19. The flow rate Q of the water to be treated 4supplied to the gas dissolved water producing apparatus 1 is measured bythe flow meter 19 and the flow rate signal 20 is sent (fed back) to thefirst controller 21. The first controller 21 determines a differencebetween a measured flow rate and a flow rate of a control target value,and sends a first flow rate control signal based on the determineddifference to the motor (not shown) for driving the pump 17, so that themotor may drive the pump 17 at the controlled revolution speed.

[0042] The PID control system is employed to control the revolutionspeed of the motor in a stepless manner such that, for example, therevolution speed is increased if the measured flow rate is lower thanthe flow rate of the control target, and the revolution speed isdecreased if the measured flow rate is greater than the flow rate of thecontrol target.

[0043] The water to be treated 4 passes through the flow meter 19, andthen a part thereof (corresponding to the flow rate Q1) passes throughthe inner side of the hollow fiber membrane 2 in the processing tank 11to flow into the first flow regulator for the water to be treated 23,and the rest of the water to be treated 4 (corresponding to the flowrate Q2) flows into the bypass piping for the water to be treated 15branched off from the supply piping for the water to be treated 13, andpasses through the flow regulator for the water to be treated 24 tobypasses the hollow fiber membrane 2. The water to be treated 4, whichhas absorbed the dissolved solution gas 3 through the hollow fibermembrane 2 while passing through the inner side of the hollow fibermembrane 2 and thus has been formed into the gas dissolved water 5, isnow exited from the inner side of the hollow fiber membrane 2 and thenflows through the gas dissolved water discharge piping 14 to join thewater to be treated 4 which has bypassed the hollow fiber membrane 2 atthe joining section 14A, and thereby the concentration of the dissolvedsolution gas in the gas dissolved water 5 is diluted, and further, thegas dissolved water 5 flows through the gas dissolved water dischargepiping 14 to be finally supplied to a cleaning equipment, (not shown).

[0044] The gas dissolved water concentration meter 26 connected to thegas dissolved water discharge piping 14 measures the concentration ofthe dissolved solution gas after the dilution, and the gas dissolvedwater concentration meter 26 then sends a concentration signal 27 to thesecond controller 28. The second controller 28 determines a differencebetween a measured concentration and a concentration of a control targetvalue, calculates a second flow rate control signal 29 based on thedetermined difference by using an incorporated arithmetic circuit,though not shown, and sends the second flow rate control signal 29 tothe first and the second flow regulators of the water to be treated 23and 24 so as to accomplish control in the following manner.

[0045] That is, in effecting control, if the measured concentration islower than that of the control target, the flow rate Q1 of the water tobe treated 4 flowing through the inner side of the hollow fiber membrane2 (the flow rate passing through the first flow regulator for the waterto be treated 23) is increased, and the flow rate Q2 of the water to betreated 4 bypassing the hollow fiber membrane 2 (the flow rate passingthrough the second flow regulator for the water to be treated 24) isdecreased. If the measured concentration is greater than that of thecontrol target, then the flow rate Q1 of the water to be treated 4flowing through the inner side of the hollow fiber membrane 2 isdecreased and the flow rate Q2 of the water to be treated 4 bypassingthe hollow fiber membrane 2 is increased. The flow rates are controlledin this manner to adjust the concentration of the dissolved solution gas3 in the gas dissolved water 31 to the prescribed value. Controlling theconcentration of the dissolved solution gas 3 in the gas dissolved water31 to the prescribed value results in controlling the pressure of thegas dissolved water 5, 31 to a prescribed pressure. It is to be notedthat, preferably, the overall gas dissolved water producing apparatus 1should be operated automatically.

[0046] If the concentration data of the water to be treated 4 and thesaturated gas dissolved water 5 are collected regularly and alternatelyat, for example, the locations indicated as B and A in the drawingrespectively and are continuously updated by using the gas dissolvedwater concentration meter 26 while the gas dissolved water 31 is notproduced, then the gas dissolved water 31 having the prescribed level ofdissolved solution gas concentration could be produced and supplied in ashort time, even in a case where a dissolved solution gas concentrationof the water to be treated 4 supplied from the source of the water to betreated 8 being changed, or in a case of the water temperature and thusthe dissolved solution gas concentration of the saturated gas dissolvedwater 5 changing.

[0047] For example, if a concentration of the solution gas desired to bedissolved, such as N₂ and O₂, in the water to be treated 4 from thesource of the water to be treated 8 is increased, a flow ratedistribution may be controlled such that the flow rate of Q1 isdecreased and the flow rate of Q2 for bypassing is increased. Similarly,if the concentration of the saturated gas dissolved water 5 isincreased, then the Q1 is decreased and the Q2 is increased. Further, ifthe water temperature of the gas dissolved water 5 is increased, thesaturated concentration of the gas allowed to remain as dissolved in thehollow fiber membrane 2 (see FIG. 2) will be substantially lowered, andthen the Q1 is increased and the Q2 for bypassing is decreased. A totalnumber of three dissolved solution gas concentration meters 26 formeasuring the concentrations of the water to be treated 4, the saturatedgas dissolved water 5, and the gas dissolved water after the dilution 31respectively, may be arranged on the basis of one for each appropriatelocation, or a single dissolved solution gas concentration meter 26 maybe employed and in that case the locations for measurement may beswitched between one another as needed. In the preceding discussion, thedissolved gas concentration meter 26 may be arranged so as to measurethe concentration and/or temperature of the gas dissolved water 31alternatively.

[0048] In the gas dissolved water producing apparatus 1 according tothis embodiment, preferably the ultrapure water to which the degassingprocess has been applied is used as the water to be treated 4. In thepresent apparatus 1, the concentration levels in the water to be treated4 at the inlet port of the supply piping for the water to be treated 13are controlled to be below 3 ppm for nitrogen, below 100 ppb for oxygen,and below 1 ppb for hydrogen respectively. The water to be treated 4 iscontrolled such that the supply flow rate Q is 20 to 30L/min, the supplytemperature is in a range of 20 to 23° C. and the supply pressure is ina range of 0.20 to 0.30 MPa (2.0 to 3.0 kgf/cm²) (by gage pressure).

[0049] The nitrogen gas (case 1) or the hydrogen gas (case 2) eachhaving an approximately 100% purity were used as the solution gas 3. Itis preferable that the solution gas to be supplied has a purity of 99%or higher. Alternatively, argon gas, oxygen gas or carbon dioxide gasmay be used as the solution gas 3. The supply pressure of the solutiongas 3 is 0.00 MPa (0.00 kgf/cm²) (by gage pressure), which is equivalentto the ambient pressure. The supply pressure of the water to be treated4 is set to be higher than the solution gas pressure by 0.20 to 30 MPa(2.0 to 3.0 kgf/cm²). Setting the supply pressure of the water to betreated 4 to be higher than the solution gas pressure by 0.01 MPa (0.1kgf/cm²) or more can supply a gas dissolved water that includes nominute air bubbles or impurities and still has a uniform concentration.Preferably, the supply pressure of the solution gas 3 is typicallyhigher than the ambient pressure, because in this case the supply methodcan be simplified.

[0050] In the present gas dissolved water producing apparatus 1, asection in contact with the liquid is made of a non-metal material so asto avoid a problem of metal ions being released into the water to betreated 4. The pump 17 is controlled in a stepless variable speedcontrolling manner, and is designed as a non-particle type using adynamic pressure bearing to eliminate any mechanical contacts of rotorsso as to inhibit generation of minute particles from the inside of thepump, and a highly purified ceramic and a tetrafluoride resin are usedfor the material of the liquid contacting section to avoid a problem ofmetal ions being released into the water to be treated 4. The filter 18has employed a membrane filter having a nominal filtration rating of0.05 μm. As for the hollow fiber membrane, it is preferable to use ahollow fiber membrane made of Teflon, a porous hydrophobic membrane(pore size distribution of 0.01 to 1 μm) made of polytetrafluoroethyleneor the like. As for the material of the piping, it is preferable to usethe piping made of PVDF (polyvinylidenfluoride, fluororesin) which hasexcellent air-tightness and a relatively low permeability against thegas from the outside.

[0051] According to the gas dissolved water producing apparatus 1 of thepresent embodiment, if nitrogen gas is used as the solution gas 3 (case1), the gas dissolved water 31 having the nitrogen gas concentration of5 to 20 ppm (at the water temperature of 20° C.) can be producedefficiently in a short period. Alternatively, if hydrogen gas is used asthe solution gas (case 2), the gas dissolved water 31 having a hydrogengas concentration of 100 to 1000 ppb (at the water temperature of 20°C.) can be produced efficiently in a short period.

[0052] FIGS. 3 to 5 show experimental results from the measurement ofthe concentrations varying over time in the case of using nitrogen gas(case 1), illustrating respectively, the case for producing the gasdissolved water 31 having a concentration of 6 ppm at a watertemperature of 20° C. (FIG. 3), the case for producing the gas dissolvedwater 31 having the concentration of 10 ppm at the water temperature of20° C. (FIG. 4), and the case for producing the gas dissolved water 31having the concentration of 13 ppm at the water temperature of 20° C.(FIG. 5). In FIGS. 3 to 5, the x-axis indicates the time (unit byminutes) and the y-axis indicates the dissolved nitrogen gasconcentration (unit by ppm). Further, in the respective drawings, thesupply flow rate of the water to be treated was set to be 20L/min andthe measurements were repeated four times, which are represented by thedata {circle over (1)} to {circle over (4)}. In respective cases, as canbe seen from the data, the gas dissolved water 31 of the targetedconcentration can be produced in a time of around 1 to 1.5 minutes.

[0053] It is to be appreciated that if the solution gas is not a 100%purified gas, the concentration of the solution gas dissolved in the gasdissolved water would be a saturated concentration based on a partialpressure of the solution gas in the supplied gas. Needless to say, thegas supplied to the solution gas supply piping may be a mixed gas.

[0054] The first flow regulator for the water to be treated 23 in thesupply piping for the water to be treated 13 may be a control valve forcontrolling the flow rate in response to the second flow rate controlsignal 29 from the second controller 28. The second flow regulator forthe water to be treated 24 in the bypass piping for the water to betreated 15 may also be a control valve for controlling the flow rate inresponse to the second flow rate control signal 29 from the secondcontroller 28. Instead of the two control valves being disposedindependently in respective pipings, a single three-way control valvefunctioning as a flow rate controlling means of the water to be treatedmay be installed in the branch section 13A of the supply piping for thewater to be treated 13. In that case, the three-way control valve servesas the first flow rate regulating means as well as the second flow rateregulating means. In this regard, the branch section 13A is consideredto be a part of the supply piping for the water to be treated 13 and apart of the bypass piping for the water to be treated 15, as well.

[0055] It is to be appreciated that the gas dissolved water producingapparatus 1 of the present invention may also be utilized as a degassedwater supplying apparatus by switching the flow directions such that allthe flow toward the supply piping for the water to be treated 13 may bedirected and passed through the bypass piping for the water to betreated 15. Further, the apparatus according to the present inventioncan also produce a saturated gas dissolved water 31 by switching theflow directions so that all the flow originally directed to the supplypiping for the water to be treated 13 can be introduced into the innerside of the hollow fiber membrane 2. Besides, although in thisembodiment, the apparatus has the configuration in which the supplypiping for the water to be treated 13 for producing the gas dissolvedwater 31 and the bypass piping for the water to be treated 15 arebranched off from the common source of the water to be treated 8, thepresent invention is not limited to the particular mode shown in FIG. 1in which the bypass piping of the processing tank 11 is provided, butone piping of the water to be treated which is connected to theprocessing tank 11 for producing the saturated gas dissolved water andthe other piping of the water to be treated for dilution may beconnected to separate sources of water to be treated so as to besupplied therefrom respectively.

[0056] An ultrasonic cleaning equipment for wafer 101, 102 will now bedescribed as an example for applying the gas dissolved water with itsconcentration controlled to be below the saturated concentration, whichhas been produced according to the present invention. The gas dissolvedwater obtained by way of the present invention is especially suitablefor cleaning device wafers.

[0057]FIG. 6 shows a perspective view of the ultrasonic cleaningequipment for wafer 101 serving as an ultrasonic cleaning equipment.Referring to FIG. 6, the ultrasonic cleaning equipment for wafer 101comprises a rotary chuck 140 having four chuck pawls 141 and a shaft 142on which the rotary chuck 140 is mounted. The rotary chuck 140 isdesigned to carry a semiconductor wafer W1 thereon with the chuck pawls141 clamping a periphery WA of the wafer W1 and to rotate in thedirection indicated by the arrow X as centered on the shaft 142. Theultrasonic cleaning equipment for wafer 101 further comprises a cleaningliquid injecting nozzle 150, and is designed such that a cleaning liquid151 may be injected from the cleaning liquid injecting nozzle 150against a surface to be cleaned WB of the semiconductor wafer W1(hereinafter sometimes referred to as an upper surface WB).

[0058] In the ultrasonic cleaning equipment for wafer 101, for example,after having been polished, the semiconductor wafer W1 is placed withthe surface to be cleaned WB up and secured clamped at the peripherythereof by the chuck pawls 141 of the rotary chuck 140. While the rotarychuck 140 is being rotated in the direction indicated by the arrow X,the cleaning liquid 151 is injected from the cleaning liquid injectingnozzle 150 against the upper surface WB of the semiconductor wafer W1 towash off abrasive grains and shavings held on the upper surface WB ofthe semiconductor wafer W1. Hereinafter, an application in the megasonic cleaning will be described.

[0059]FIG. 7 is a sectional view illustrating a detailed configurationof a mega sonic cleaning nozzle 155 used in the ultrasonic cleaningequipment for wafer 101 of FIG. 6. Referring to FIG. 7, the mega soniccleaning nozzle 155 is configured such that an ultrasonic vibrator 157is mounted on a rear end portion 156C of a nozzle main body 156 so as tofunction as an ultrasonic wave transmitting device. When the ultrasonicvibrator 157 is activated and the gas dissolved water 31 (see FIG. 1)from the gas dissolved water supply line 14 (see FIG. 1), after theconcentration thereof having been adjusted as shown in FIG. 1, isintroduced into an inlet port 156A formed in the nozzle main body 156,thereby an ultrasonic vibration energy is imparted to the gas dissolvedwater 31, so that the cleaning liquid 151 (see FIG. 6) to which theultrasonic vibration energy has been imparted can be injected from aninjection port 156B formed in the nozzle main body 156 against the uppersurface WB of the semiconductor wafer W1. It is to be noted that the gasdissolved water 31 is injected as the cleaning liquid 151.

[0060] In this way, the ultrasonic energy is indirectly imparted to anydust existing on the upper surface WB of the semiconductor wafer W1through the injected cleaning liquid 151 (see FIG. 6). As a result, thedusts on the semiconductor wafer W1 are vibrated and released from theupper surface WB of the semiconductor wafer W1, which will be washedaway by the injected cleaning liquid 151.

[0061] In this case, a gas dissolved water containing, for example, N₂as the solution gas may be used as the cleaning liquid, and in that caseair bubbles are liable to be formed in the cleaning liquid if theconcentration of the gas dissolved therein is too high. In such an eventthat the generated air bubbles gather to form large air bubbles and/orthe generated air bubbles adhere to the surface being cleaned WB, theportion of the semiconductor wafer W1 having the air bubbles adheringthereto is prohibited from being cleaned uniformly as compared to theother portions of the wafer W1 having no air bubbles adhering thereto.

[0062] To deal with this case, if the gas dissolved water with itsconcentration controlled to be equal to or less than the saturatedconcentration is used in the above-discussed mega jet cleaning, as isthe case with the present invention, it may help inhibit the formationof such air bubbles, or, if any, the formation of the air bubbles ofparticularly large diameter may be limited, and thereby cleaning of theminute concavities and convexities on the device wafer havingmicro-fabricated patterns may be performed in a gentle and uniformmanner. In other cleaning cases, preferably the gas dissolved water withthe concentration not greater than the saturated concentration should beused to clean a device wafer particularly having a micro-fabricatedpatterned surface.

[0063]FIG. 8 shows another ultrasonic cleaning equipment for wafer 102as an alternative embodiment of the ultrasonic cleaning equipment. Theultrasonic cleaning equipment for wafer 102 comprises a gas dissolvedwater producing apparatus 1, a cleaning bath 163, a cleaning liquidsupply line 160 interconnecting the gas dissolved water producingapparatus 1 and the cleaning bath 163, and a drain tank 170 arranged tohouse the cleaning bath 163 therein.

[0064] A gas dissolved water 31 (e.g., nitrogen containing water) withthe concentration thereof controlled to be not greater than thesaturated concentration, which has been produced in the gas dissolvedwater producing apparatus 1 of the present invention, is supplied intothe cleaning bath 163 from a cleaning liquid supply nozzle 162 attachedthereto via the gas dissolved water supply line 160.

[0065] The cleaning liquid supply nozzle 162 (see FIG. 9) is acylindrical nozzle lying along an inner bottom surface 164 of thecleaning bath 163. This cleaning liquid supply nozzle 162 includes aplurality of discharge ports 165 along a longitudinal direction thereof(see FIG. 9), and the gas dissolved water 31 is supplied as the cleaningliquid 31 from the discharge ports 165 into the cleaning bath 163. Anultrasonic vibrator 166 functioning as an ultrasonic wave transmittingdevice is disposed on a lower face 169 of the cleaning bath 163, and theultrasonic vibrator 166 imparts the ultrasonic vibration energy to thecleaning liquid 31 in the cleaning bath 163.

[0066] Typically, 25 device wafers W2 to be cleaned (for example,silicon wafers) are placed in the cleaning bath 163 in the verticallyupright position. Then, the cleaning bath 163 is filled with thecleaning liquid 31 and cleaning liquid which overflows from the cleaningbath 163 is recovered in the drain tank 170 arranged to house thecleaning bath 163 therein. The cleaning liquid 31 recovered in the draintank 170 is discharged from the drain line 167 connected to the draintank. The ultrasonic cleaning equipment for wafer 102 of this embodimentprovides an advantageous effect that a large number of device wafers W2can be cleaned quickly thereby improving a throughput, in addition tothe advantages similar to that provided by the preceding ultrasoniccleaning equipment for wafer 101.

[0067] Advantageous Effects of the Invention

[0068] As discussed above, since the gas dissolved water producingapparatus according to the present invention comprises the solution gassupply channel, the first supply channel for the water to be treated,the second supply channel for the water to be treated and the gasdissolved water discharge channel, and the second supply channel for thewater to be treated joins the gas dissolved water discharge channel sothat the water to be treated guided by the second supply channel for thewater to be treated can dilute the gas dissolved water until theconcentration of the solution gas in the gas dissolved water reaches aprescribed concentration, the gas dissolved water producing apparatus isable to produce rapidly and efficiently a gas dissolved water that has aconcentration of dissolved solution gas not greater than a saturatedconcentration.

[0069] As discussed above, since the ultrasonic cleaning equipmentaccording to the present invention comprises the gas dissolved waterproducing apparatus of the present invention and the ultrasonic wavetransmitting device, and when a workpiece to be cleaned is cleaned withthe gas dissolved water produced by the gas dissolved water producingapparatus of the present invention, the ultrasonic energy is imparted tothe gas dissolved water, therefore the gas dissolved water controlled tohave a saturated concentration suitable for cleaning can be used as acleaning liquid, and further, a gas dissolved water to which theultrasonic energy has been imparted can be used as a cleaning liquid, sothat the workpiece to be cleaned can be cleaned more cleanly.

1. A gas dissolved water producing apparatus, in which a solution gas isdissolved in water to be treated so as to produce a gas dissolved water,said apparatus comprising: a dissolving section for dissolving asolution gas into a water to be treated; a solution gas supply channelfor guiding the solution gas into said dissolving section; a firstsupply channel for the water to be treated for guiding the water to betreated into said dissolving section; a gas dissolved water dischargechannel for guiding the gas dissolved water from said dissolvingsection; and a second supply channel for the water to be treated forguiding the water to be treated without passing through said dissolvingsection, wherein said second supply channel for the water to be treatedjoins said gas dissolved water discharge channel, and the water to betreated which has been guided through said second supply channel for thewater to be treated dilutes the gas dissolved water so that aconcentration of the solution gas dissolved in the gas dissolved watercan be controlled to a prescribed level of concentration.
 2. A gasdissolved water producing apparatus in accordance with claim 1, in whichsaid second supply channel for the water to be treated is branched offfrom said first supply channel for the water to be treated so as to forma bypass channel for bypassing said dissolving section.
 3. A gasdissolved water producing apparatus in accordance with claim 1 or 2, inwhich said dissolving section comprises a hollow fiber membrane, whereinthe solution gas is introduced into one side of said hollow fibermembrane, and the water to be treated is introduced into the other sideof said hollow fiber membrane so as to generate the gas dissolved water.4. A gas dissolved water producing apparatus in accordance with any oneof claims 1 to 3, said apparatus further comprising: either one of afirst flow rate regulating means or a second flow rate regulating means,said first flow rate regulating means being disposed in said firstsupply channel for the water to be treated at a downstream side of saidbranch section or in said gas dissolved water discharge channel at anupstream side of a joining section where said second supply channel forthe water to be treated joins said gas dissolved water dischargechannel, and functioning to regulate a flow rate of the water to betreated flowing through said dissolving section, and said second flowrate regulating means being disposed in said bypass channel andfunctioning to regulate a flow rate of said water to be treatedbypassing said dissolving section; a dissolved solution gasconcentration measuring means disposed in said gas dissolved waterdischarge channel at a downstream side of said joining section formeasuring a dissolved solution gas concentration in the gas dissolvedwater; and a second control means for controlling said either one ofsaid first flow rate regulating means or said second flow rateregulating means, whichever has been disposed, based on the dissolvedsolution gas concentration measured by said dissolved solution gasconcentration measuring means, so that the dissolved solution gas can becontrolled to a prescribed level of concentration.
 5. A gas dissolvedwater producing method, comprising the processes of: a first process forintroducing a solution gas into a dissolving section where the solutiongas is to be dissolved into a water to be treated: a second process forintroducing a water to be treated into said dissolving section; a thirdprocess for dissolving the solution gas into the water to be treated insaid dissolving section to produce a gas dissolved water; and a fourthprocess for mixing the water to be treated not passing through saiddissolving section into the gas dissolved water so that the solution gasdissolved in the gas dissolved water after the mixing process can becontrolled to a prescribed level of concentration.
 6. A gas dissolvedwater producing method in accordance with claim 5, in which: saidcontrol in said fourth process is performed by controlling a ratio of aflow rate of water to be treated passing through said dissolving sectionto the flow rate of the water to be treated not passing through saiddissolving section.
 7. An ultrasonic cleaning equipment, comprising: agas dissolved water producing apparatus as defined in any one of claims1 to 4; and an ultrasonic wave transmitting device for impartingultrasonic energy to a gas dissolved water when a workpiece to becleaned is cleaned with the gas dissolved water produced by said gasdissolved water producing apparatus.
 8. An ultrasonic cleaning method,comprising the processes of: a producing process for producing a gasdissolved water according to the gas dissolved water producing method asdefined in the claim 5 or 6; an energy imparting process for impartingultrasonic energy to the gas dissolved water which has been produced bysaid producing process; and a cleaning process for cleaning a workpieceto be cleaned, by using the gas dissolved water to which the ultrasonicenergy has been imparted in said energy imparting process, as a cleaningwater.